ACTION OF A COIL OUTSIDE THE AXIS. 



95 



For a coil of thickness dr, the winding of which is uniform, n^ 

 may be replaced in these expressions by n\dr. Integrating then in 

 respect of r, from a' to a", we shall have the components X and Y of 

 the magnetic action of a coil of thickness a" - a', which gives 



(34) 



1 



dr . 



The first term X of the value X, obviously represents the 

 action on the axis given by equation (12). 

 The value of the second term, X, is 



x-b 



As we have 



we get 



T r'-At 



r r - 



' 



The first term of y is 

 Y 



A similar expression has already been previously integrated (730), 

 and we have 



a + 



a' + Ja' 2 + (x + b}* 



